Fluorescent lamps have replaced incandescent lamps for lighting purposes in many areas because the fluorescent lamps provide an equal or greater amount of visible light while consuming less energy compared to the incandescent type. A current, commercial fluorescent lamp generally comprises a long tube containing a drop of mercury, a small amount of argon gas and electrodes sealed into each end of the lamp. Additionally, the fluorescent lamp has filaments on its opposite ends. The inner surface of the tube is coated with a light emitting substance usually fluorescent or phosphorescent metallic salts. The lamp emits light when an electrical arc is created through the argon gas and mercury. This arc produces a large amount of ultraviolet light radiation, in the invisible range of the light spectrum. The ultraviolet light radiation then strikes the fluorescent substance to emit radiation having a longer wavelength. The generation of the arc is due to the ionization of the argon gas which requires that a high voltage called the breakdown voltage be applied between the electrodes. Once started, only a low maintaining voltage is necessary to maintain the ionization process. Thus, the breakdown voltage is necessary to start or ignite the fluorescent lamp while the maintaining voltage is necessary to maintain the ionization within the fluorescent lamp. If the voltage between the electrodes decreases below the maintaining voltage, the argon gas within the fluorescent lamp begins to deionize and the current through the lamp eventually drops to zero. The deionization time is generally twenty to forty microseconds during which the current through the lamp will decay considerably slower than the voltage. Therefore, the current will lag the voltage. Additionally, after the voltage between the electrodes has become zero there will still be a current through the lamp for a few microseconds.
A fluorescent lamp requires an element which will initially provide the breakdown voltage and thereafter limit the current through the lamp. This element is called a ballast and could be constructed with an inductor and switch. A more sophisticated circuit could be constructed by using active elements. The simple ballast is not very expensive but produces a low efficiency of energy transfer. The sophisticated ballast is usually expensive, not very reliable, and capable of producing electromagnetic interferences. Additionally, the high voltage that persists even when the lamp is removed poses a measure of danger to safety.
The electronic ballast includes a first and second socket for electrically engaging the lamp filaments, and an energy storing component for storing energy from the voltage source and selectively transmitting energy to the lamp. Additionally, the ballast includes a component for controlling the transmission of energy to the lamp with the controlling component having a first state for enabling energy to be stored in the energy storing component and enabling energy to be transmitted from the voltage source to the lamp, and a second state for enabling the energy stored in the energy storing component to be transmitted to the lamp whereby the transmission of energy from the voltage source to the lamp is prevented. The first socket is connected between the voltage source and the energy storing component, and the second socket is connected between the energy storing component and the controlling component so that the filaments are connected in series to the energy storing component. The energy storing component and controlling component cause the generation of the breakdown voltage to ignite the fluorescent lamp when the lamp is not ignited and the controlling component is in the second state. Additionally, the energy storing component enables constant current to flow through a portion of the energy storing component when the lamp is ignited and the controlling component is in the second state. This enables the present invention to consume very little energy, thereby increasing the efficiency of energy transfer to the lamp.
Because ballasts of the present invention utilize only small number of electronic components, the costs for the ballast are very low. Additionally, the present invention produces low electromagnetic interferences and enables the voltage across the lamp to be equal to or less than the maintaining voltage after the lamp has ignited. In fact, the voltage across the lamp drops to zero if the lamp is removed thereby providing protection against electrical shock.